AddNetworkFragment bottom buttons align parent bottom,
it has display problem because collapsing toolbar changes
its height and squeeze the bottom buttons out of the screen.
This change sets the bottom buttons align the bottom of
other content.
Bug: 179656154
Test: manual visual
Change-Id: I6f0062d10c603e40e3f8c2683d5610418df6522a
WifiDialog.java can be launched as "full screen mode"
in some use cases. However the way it's done is that
it uses theme to fake the full screen appearance.
It just feels hacky to use a dialog for full screen UI.
So, we created an "AddNetworkFragment" to make this
page can look like a normal fragment.
Also, clean up some useless code about "full screen mode"
of WifiDialog.
Change-Id: Iedd04c6a8e403cbceb872313314e1cba0d514246
Fixes: 111875856
Test: robo test, manual test
